Man. You could build THAT bike... maybe later
I'm not sure what the consensus is, but for what it's worth I've been real happy with my Grubee Skyhawk Stage III, 4 Stroke Huasheng 49cc. I purchased it well broken in, and in the four months I've owned it, ridden nearly 100 miles. Honestly, I'm still getting it where I want it before paint.
I would suggest upgrading your rear hub/ sprocket/ brakes, right from go. There's lots of discussion here concerning that. Wish I could give you some guidance on sourcing, but I am unable. Hang in there, you'll have all the suggestions you can handle!